1. Field of the Invention
The present invention relates to an optical device such as an organic EL (electroluminescent) display.
2. Description of the Related Art
Since organic EL displays are of self-emission type, they have a wide viewing angle and a high response speed. Further, they do not require a backlight, and therefore, low profile and light weight are possible. For these reasons, the organic EL displays are attracting attention as a display which replaces the liquid crystal display.
An organic EL element, which is the main part of the organic EL displays, includes a light transmitting front electrode, a light reflecting or light transmitting back electrode facing the front electrode, and an organic layer interposed between the electrodes and containing a light emitting layer. The organic EL element is a charge-injection type light emitting element which emits light when an electric current flows through the organic layer.
In order to display an image on an organic EL display, it is necessary that light emitted from its emitting layer be output from the front electrode. However, of the light travels toward the front side in the element, the portion which travels in a wide-angle direction is totally reflected on the interface of the front electrode. For this reason, a great portion of the light emitted by the organic layer cannot go out of the organic EL element.
As illustrated with the organic EL display, displays in which each pixel has a light emitting element entail the drawback in which the outcoupling efficiency of the light emitting element is not sufficient. In addition, in achieving the present invention, the present inventors have found that the luminous efficiency of such a display is greatly influenced by not only the outcoupling efficiency of the light emitting element, but also other factors.